Calorimetric Studies of the Fusion of Linear Polyethylene

Abstract

Recent advances in instrumentation, as exemplified by the Perkin-Elmer Differential Scanning Calorimeter,⁽¹⁾⁽²⁾ have enabled calorimetric studies to be made on molecular weight fractions of crystalline polymers since only small amounts of sample are required. Recently, the extremely important influence of molecular weight in governing all aspects of the crystallization behavior of polymers and in allowing for a critical interpretation of morphology, including the interfacial structure, has been pointed out.^(3)(4)(5) As a prelude to discussing the fusion properties of linear polyethylene, as observed calorimetrically, and their dependence on molecular weight, morphology, and mode of crystallization it is appropriate to examine certain of the operational aspects of the instrument. This involves the absolute calibration of the instrument itself and an assessment of the effect of polymer mass, heating rate and scale factor on the measured enthalpy of fusion with particular concern for the base line delineation and the detection of the onset of melting. For the calibration, the enthalpy of fusion of indium is taken as 6. 8 cal. /g. Detailed studies have shown that the area under the fusion curve is in direct proportion to the indium mass and, for the DSC-1B, is inversely proportional to the degree of attenuation. Gray⁽⁶⁾ has shown that using the above value of ΔH* for indium, the corresponding values obtained for tin, lead, zinc, and a variety of organic compounds agree almost exactly with the values quoted in the literature as obtained by conventional calorimetry. This is also quantitatively shown by the work of Yoncoskie⁽⁷⁾ in the present symposium.